Anti Vibration Mountings

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Technology

With a relatively hard machine support or mounting, theamplitude of the installed equipment is minimal, but theresulting isolation efficiency is much less than with a moreresilient mounting. Although technically the isolation effi-ciency of a soft mounting is very high, it impairs themachine stability and can lead to uncontrolled operation ofthe installation (example: distorted frames on productionmachines). Hence, for the machine type in question, an idealcompromise must be sought between the level of the isolationefficiency and permissible spring deflection. As a generalrule the mountings of machine tools, machining centers etc.should be hard whilst those for equipment such as com-pressors, generators and pumps etc. should be relatively

soft. Rubber as an elastic medium is probably the mostuniversal material used for vibrational damping.

Steel spring(no self-damping)

TimeRubber spring

(self-damping)

Its special properties render it particularly suitable for dam-ping and springing elements. Rubber elements can acceptconsiderable overloads for a short time without suffering anydamage. In contrast to steel springs, under dynamic loading,rubber elements convert the energy absorbed into heat byinternal molecular friction.This process known as damping is continuous and it isalways required whenever resonance can occur or shockshave to be reduced quickly.

Two basically different types of rubber loading were madeuse of in the design of ROSTA anti-vibration mountings: pure tensile or pressure loading for the anti-vibration

mountings of the types V, ISOCOL and N. These relativelysimple elements cover the medium natural frequency bandbetween 15 and 30 Hz.

loading via lever of pretensioned rubber elements bytorsional or flexing motion of the ROSTA rubber suspens-ion units in so-called spring dampers. This system allowsthe construction of anti-vibration mountings in the lowfrequency range between 2 and 10 Hz. These are typesESL and AB.

The following survey of the entire product range shows theadvantages and applications of the various types. For com-plex applications and in the case of queries, do not hesitate

to get in touch with us our technical service department isat your disposal.

Superior Technology

isolatinginalldirections

widefrequency range

freestanding

ormountingbybo

lts

selfadhesive

onbothside

s

efficientabsorption

unique

levellingsystem

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Fig. 3

15 30 45 60 75 90 %

0

21.5 1.6 1.8 2.2 3 10

Fig. 2

Technology

Oscillations

Shocks

Tremors

Fig. 1

Frequency ratio

= Interfering frequency (machine)Natural frequency (damper)

Degree of isolation

Acoustic isolation ratio Steel 1 : 1related to steel: Bronze 1 : 1.3

Cork 1 : 400Rubber 1 : 800Air 1 : 90000

Fig. 5

Isolation of Vibrationsand Solid-borne Noise

There are basically three different forms of vibration, asshown in fig. 1.The overcritical type of mounting is used for isolating vib-rations and tremors, while for isolating shocks the sub-critical type of mounting is generally employed.

Overcritical:Interfering frequency (machine)

= > 1

Subcritical: Interfering frequency (machine) = < 1

Mechanical Vibrations

The basic principle of vibration isolation technique is toisolate the source of interference, or the object to be pro-tected, from its surroundings. This is achieved by suitablefrequency adaption the higher the frequency ratio, thehigher the degree of isolation. See fig. 2.

Absorptionof Solid-borne NoiseWhile interference forces are isolated on the basis ofvibrational theory, the isolation of sound transmissionthrough solid-borne bodies is governed by the laws of wavemechanics. The isolation efficiency depends on the acousticstiffness of the contacting materials between machine andstructure. The table in fig. 3 shows the absorption efficiencyof some material. A steel rubber compound normally offers ahighly efficient isolation of the solid-borne noise.

Damping

In the ROSTA type mounts is damping a function of the in-ternal molecular friction in the rubber material during oscil-lation and vibration. The resulting energy loss is convertedinto heat during the vibration process. The area (fig.4)between the loading and unloading curves corresponds tothe energy loss or damping in the ROSTA elements.In practice, the damping characteristic becomes importantwhen the vibrations of an elastically supported machine ispassing through the resonance field and an oscillationcould build up. The natural isolation properties of theROSTA anti-vibration mountings limit this build-up to aminimum due to the high energy loss. Vibrations areabsorbed as soon as they occur.The amplitude/time characteristic demonstrates the highefficiency of the rubber damping material.

Natural frequency (damper)

Natural frequency (damper)

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ountings

Loss of energyper cycle

Unloa

ding

Loading

Deflection

Time spaceAm

plitude

Load

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Technology

Natural frequency a = . = Hz

Fig. 6

Fig. 8

Fig. 9

Fig. 7

Natural Frequencyof the Vibration Damper

Even simple applications require some elementary know-ledge of vibration isolation. An important factor in thisconnection is the natural frequency of the damper which ismeasured in rpm or Hz, i.e. the number of oscillations perminute or second which lead to resonance excitation.The natural frequency n

eis a function of the spring travel s

(in.) under a load G (lbs.) and can be calculated from theformula given in fig. 6.

Natural Frequency with Parabolic SpringCharacteristic

It is only with vibration dampers comprising steel springs thatthe dampers natural frequency can be derived directly fromthe measured spring travel according to the formula in fig. 6.Steel springs have a linear characteristic and hence a springconstant. But they have no damping and are only suitable forpure swing mountings.

All other damping materials such as rubber, cork etc., aredeformed under load and the effective measured springtravel is greater than the actual resulting natural frequency.Rubber springs have a slightly parabolic characteristic andthe natural frequency resulting from the applied load istherefore essentially higher than the calculated value inconformity with the spring travel (fig. 7: s

1determines the

frequency). The following catalogue frequency values aremeasured and derived from the s

1spring travel.

Hence the natural frequency values must lie outside theresonance field. An undesirable build-up of vibrations islikely to occur wherever the exciting frequency n

errand

natural frequency neare the same.

damping is not exactly definable and solid-bornenoise isolation is reducedoscillation build-up, peak values depending on self-

damping D within the resonance fieldvibration isolation efficiency dependent on ,also efficient solid-borne noise isolation

Cold Flow

During the course of time, all elastic materials deform moreor less permanently under load, which becomes apparentby a slight increase in deflection and cold flow. This coldflow exhibits a linear characteristic on a logarithmic timebase. The diagram in fig. 9 shows that more than half ofthe total cold flow occurring in one year has taken placeafter loading for one day. The max. setting of ROSTA anti-vibration mountings is approx. +10% of the nominalspring travel according to the catalogue.

< 1:

= 1:

>2:Proportion of frequency =

nerr

ne

Time range in sec.

Pitch of spring s

Abscissa

21

s [in.]12 . 32.16

or . = rpm260

s [in.]12 . 32.16

LoadFinlbs.

S1

TransmissibilityV=

transmittedpower

excitedpower

1 3 4 52

assumed load F

Ordinate

Tang

ent

1

0.8

0.6

0.4

0.2

2

6 6x101 6x102 6x103 6x104 6x105 6x106 6x107

1stday

1styear

First deflectionunder load

Cold flow

(20%)

(40%)

(60%)

(80%)

Isolation range

D=1.0

D=0.25

D=0

sub-critical

function

overcritical

function

Damping

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Resonance

A


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Fig. 12

Technology

A, B, C, D Mounting points of anti-vibration mountingsS Center of gravity

Fig. 10

Active isolation

Fig. 11

Passive isolation

Fig. 12

Active and Passive IsolationIn practice, elastic intermediate supports or mountings are in-stalled for two different reasons:

Practical ConsiderationsThe use vibration damping machine mountings and supportspermits continuously flexible installation of a machine line.Conventional floor anchorages can be almost totally dispen-sed with and the machines rapidly and simply converted tonew production sequences. Furthermore, the normally stan-dard integrated levelling facilities are a simple way to com-pensate for uneven floor surfaces.

Protective ConsiderationsPersonnel, environment, building structure and the machinesthemselves are efficiently protected by the vibrationcompensating machine supports. Vibrations and shocksare considerably reduced and the working environmentimproved.

Active or direct isolation signifies the damping of thevibrations and shocks from an operating machine, i.e. to pre-vent vibrations being transferred to foundation, adjacentrooms, building etc. To be taken into account in each casehere are the interfering frequency, the machine structure and

its site. This is the most frequent type of vibration isolationand occurs in almost all factories or households.

Passive or indirect isolation signifies the shieldingof sensitive equipment such as weighing and measuring in-struments, laboratory appliances etc. from vibrationsand shocks. Here the technical requirements can be highlydependent on the environment since interference is often ex-ternal in origin; from the street, railways or large buildingsites. The assistance of the specialist engineer is frequentlynecessary to define this spectrum.

Defining the Supporting

Forcesa) Position of ROSTA anti-vibration mountingson/under the machine frame

Install all elements so that the loading or spring travel isuniform. Whenever as so often in practise asymmetriccenter of gravity circumstances and hence differing loadsand spring travels are encountered, the supporting forcescan be determined according to fig. 12. In such cases, dif-ferences in spring travel are to be equalized with the aid ofspacer plates.

Load on point A = S b d ca d

D = S a b ca d

B = S a b d ca d

C = S b ca d

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Product Range

ROSTA Anti-vibration MountingType ESLROSTA anti-vibration mountings type ESL are intended for theabsorption of medium and low frequency vibrations and are de-signed to accept compression, tension and shear loading as wellas combined loadings. They can be installed in any desiredposition and are also ideal for ceiling and wall mounting. Due tothe mechanically secured principle of the anti-vibration mountingstype ESL no tearing off is possible. These elements are mainte-nance-free, insensitive to water and dirt and suitable fortemperatures from 40 to + 180 F. The housing and core of the elements up to size45 are made of light alloy with steel brackets. The housing of size50 is made of GGG 40. All elements are paint-finished.

ROSTA Anti-vibration MountingType VROSTA anti-vibration mountings type V are multi-directionaldampers and are designed to accept compression, tension andshear loading as well as combined loadings. They can be installedin any desired position and are also ideal for ceiling and wallmounting. Due to the mechanically secured principle of the anti-vibration mountings type V no tearing off is possible. These ele-ments are maintenance-free, insensitive to water and dirt andsuitable for temperatures from 40 to + 180 F. The core is madeof light alloy, the outer housing and brackets of steel. All elementsare paint-finished.

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A AX

B C D E F H J K L N max.

25 214 ESL 15 0.00 89.92 2.13 1.73 3.35 1.93 0.39 2.56 0.28 3.56 0.08 0.22 1.00 2.30 0.06 0.7925 215 ESL 18 67.44 269.77 2.56 2.05 4.13 2.36 0.49 3.15 0.37 4.35 0.10 0.22 1.22 2.72 0.07 1.3725 216 ESL 27 224.81 449.62 3.46 2.83 5.51 2.80 0.59 4.33 0.45 5.83 0.12 0.31 1.73 3.36 0.10 2.8225 217 ESL 38 404.66 786.84 4.61 3.66 6.89 3.86 0.69 5.51 0.55 7.17 0.16 0.28 2.36 4.61 0.14 7.5025 218 ESL 45 719.39 1348.86 5.63 4.53 8.66 4.72 0.98 6.69 0.71 9.23 0.20 0.57 2.87 5.43 0.17 11.5725 219 ESL 50 1236.46 2023.29 6.50 5.28 8.66 5.59 0.98 6.89 0.71 9.45 0.24 0.59 3.09 6.42 0.19 22.05

Anti-vibration Mounting Type ESL

Fig. a

ApplicationsFor active and passive isolation of vibrations and maximumdamping of solid-borne noise transmission in: weighbridgesand scales, measuring systems, control equipment, rotarymachinery such as compressors, refrigerating systems,blowers, pumps, mills, mixers, shock-absorbent buffers, etc.

For installation guidelines see

Multi-directional mountfor compression, tension

and shear loading

The elements must generally beinstalled in the same direction

Fig. a) Dynamic forces longitudinal

Fig. b) Dynamic forces lateral

Fig. c) Wall mounting

Fig. c

The max. load on X X axes is the double value from Z Z axes.The max. load on Y Y axes is 20% from Z Z axes.

Load un- max. WeightUPC # Type G in lbs. loaded load in lbs.

Fig. b

Load on compression in lbs.Load capacityNatural frequency in Hz674.4

562.0

449.6

337.2

224.8

112.4

0

0 0.20 0.39 0.59 0.79

3372.1

2248.1

1124.0

0

0 0.39 0.79 1.18

Load on compression in lbs.Load capacityNatural frequency in Hz

Deflection in in Deflection in in

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A B C D E F M N H J K

53 373 V 15 1300 179.85 1.93 3.15 2.01 0.49 2.17 0.37 M 10 2.30 0.12,00.79 0.390 0.6657 653 V 18 1134.89 359.70 2.60 3.94 2.44 0.49 2.95 0.37 M 10 2.91 0.14 1.18 0.51 1.5457 654 V 27 292.25 674.43 3.31 5.12 2.87 0.590 3.94 0.45 M 12 3.36 0.16 1.57 0.57 2.7657 655 V 38 584.51 1124.05 4.13 6.10 3.94 0.69 4.72 0.55 M 16 4.61 0.20 1.77 0.69 5.4057 656 V 45 1011.65 1798.48 5.00 7.48 4.80 0.980 5.51 0.71 M 20 5.830 0.24 2.36 0.89 10.2363 661 V 50 1348.86 2697.72 5.91 5.51 5.91 0.79,0 3.94 M 20 10.31 0.39 2.76 0.98 16.45

Anti-vibration Mounting Type V

Multi-directional mountfor compression, tension

and shear loading

Fig. a) Dynamic forceslongitudinal

Fig. b) Dynamic forceslateral

Fig. c) Dynamic forcesundeterminant

ApplicationsFor active and passive isolation of vibrations and dampingof solid-borne noise transmission in crushing plants, com-pressors, blowers, pumps, rotary converters, generators,mills, crane track supports, etc.

For installation guidelines see

Alternativmounting position

Type V 15 45 Type V 50

The max. load on Y Y axes is 10% from Z Z and X X axes.Momentary shock loads of 2.5 g in Z Z and X X axes are admissible.

WeightUPC # Type Load G in lbs. in lbs.

Anti-vibrationM

ountings


449.6

359.7

269.8

179.8

89.9

0

0 0.02 0.04 0.06 0.08 0.1

Deflection in in. Deflection in in.


0 0.04 0.08 0.160.12

3372.1

2248.1

1124.0

ROSTA

Fig. a

Fig. c

Fig. b

0.71x1.18

8.35

10.31


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Hydraulic pump on type V (wall fixation) Chain feeder on type V Belt conveyor suspension with type V(ceiling fixation)

Continuous newspaper folding machine on type N Air compressor on type V

Assembling robot on type N Assembling line on type N

Installations

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ountings

ROSTA

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Anti Vibration Mountings